Soil phosphorus availability and utilization efficiency by soybean [Glycene Max. (L.) Merr.] under a short term no-till in smallholder farms in South Africa

Abstract

The main limiting factor in soybean production in South Africa is low native soil phosphorus (P) availability and poor utilization efficiency of added P. Phosphorus fertilization, use of improved or high yield potential cultivars and appropriate cropping systems could increase soybean yields. The objective of this study was to determine the effects of tillage, cultivar and fertilization levels on nutrient uptake and P use efficiency, as well plant growth, yield, grain protein and oil content, in a soybean cropping system. The study was conducted under dryland conditions at Sheepmoor, Mpumalanga. A field experiment was established in a randomized complete block design. Treatments were arranged in a 2 x 3 x 3 split-split-plot structure. There were two tillage systems [no-till (NT) and conventional tillage (CT)], three cultivars (PAN 1614R, PAN 1521R and PAN 1532R), and phosphorus rate (0, 30 and 60 kg/ha). All treatment combinations were replicated three times. Phosphorus application rate, tillage and cultivar had significant effects (P < 0.05) on NPK uptake, Partial factor productivity (PFP), grain yield and soybean yield attributes. P uptake improved with P application at 30 and 60 kg/ha although it was statistically similar whilst PFP was significantly higher at 30 kg/ha P. Interactions of the main treatments did not significantly affect P uptake and PFP. There were statistically significant interactions between P application rate, cultivar and tillage on soybean yield. Yield was significantly higher at 30 kg/ha P application under NT. P application at 30 and 60 kg/ha significantly reduced oil content by 11.3% and 7.16% respectively, but had inverse effects on protein content. The activities of acid phosphatase (ACP) and alkaline phosphatase (ALP), concentrations of soil Ca, Mg, N, P, K and total P also increased with P application. Improvement of soybean yield and its attributes, grain quality, P uptake, PFP, soil physicochemical and microbial properties emphasize the need for fertilizers and sustainable cropping systems. Therefore, no-till and application of fertilizers improves soil fertility and soybean yield under small farm conditions.